This invention relates to a pneumatically powered torque impulse delivering tool for tightening screw joints and the like.
In particular, the invention concerns an impulse tool which comprises a housing with a forward impulse chamber, a rear motor chamber with a cylindrical inner wall and including a vane type air motor, air inlet and outlet passages extending from the rear end of the motor, a hydraulic impulse generator rotatively supported in the impulse chamber, wherein the motor includes a cylinder with three or more air communication openings whereof at least one permanently acts as an outlet opening means, and a vane carrying rotor drivingly connected to the impulse generator.
In tools of the above type, there is always a problem to obtain an efficient enough cooling of the impulse generator, because heat generated during operation of the tool tends to expand the fluid volume in the impulse generator such that leakage occurs, and when the tool is cooling down after a period of use air penetrates into the impulse generator. The output power of the tool is drastically impaired by air sucked into the impulse generator in this way.
A previously known way of solving this heat problem is to use the cold exhaust air from the air motor to transport heat from the impulse generator to the outside of the tool housing. An example on that is illustrated in U.S. Pat. No. 4,418,764. The tool shown in this patent is of the pistol handle type in which the housing is formed with an exhaust air passage that extends from the motor, past the impulse generator and out into the atmosphere via outlet openings at the forward end of the tool housing. The exhaust passage extends from a number of outlet openings on the motor cylinder and through cavities formed in the housing, and since there is no particular requirement in a pistol type tool to keep down the outer diameter of the housing, it has been easy just to design the casting of the housing to comprise the space necessary to accomplish a desired exhaust air flow.
In the straight type of tools, however, i.e. tools without a pistol grip handle, the outer diameter of the tool housing has to be kept relatively small to offer a comfortable grip for the operator. When in such tools it also becomes desireable to arrange air passages not only to and from openings in the motor cylinder, but past the motor from the impulse chamber to an exhaust passage at the rear end of the tool, there is a problem to obtain passages with large enough flow areas. By using the technique illustrated in the above referred U.S. patent, namely to form the passages on the inside of the housing, by casting, the manufacturing costs of the tool would be considerably increased compared to presently available tools of the straight type.
On the other hand, if the air passages for the above described cooling purposes were formed on the inside of the housing by milling or similar working, which is a commonly used method at manufacturing housings for the straight type of tools, the air passage areas would be too small or a more slender motor should have to be used for a given desired outer diameter of the housing. This method would also result in a heavier housing with smaller and less effective seal portions between the passages. In particular, this would be the case when using a reversible twin chamber type of vane motor which has a larger number of air communication openings than the commonly used single chamber type motor.